Process for treating cellulosic material



Patented Mar. 6, 1928.

UNITED STATES.

PATENT OFFICE.

FREDERICK CARL NIEDEBHAUSEB AND HAYDEN BENJAMIN KLINE, OF CLEVELAND, OHIO, ASSIGNORS TO THE INDUSTRIAL RAYON CORPORATION, OF CLEVELAND,

OHIO.

Io Drawing.

This invention relates to the application and use of relatively small amounts of combinations of the alkali metals with zinc, of which the alkali metal zincates are perhaps the best known, in the ra on artificial filament art, and to metho s for" roducin' rayon wherein combinations of al ali meta and zinc or alkali metal zincates are employed in order to produce in the finished l0 rayon material desirable roperties as will be more s ecificall detailed in thisspecification. hese al li-zinco compounds are rather loosely characterized chemical bodies,

and may be formed by dissolving metallic l6 zinc, zinc oxide, zinc hydroxide orother zinc compound, or water-soluble zinc salts such as zinc chloride, zinc nitrate or zinc sulfate in solutions of the alkali metal hydroxides to form the zincatedesired. These l0 zincates or solution of zinc in alkali metal as sodium hydroxide is the alkali metal hydroxide used for the treatment of cellulose in present day viscose manufacture, the description herein will be limited to the application of sodium zincate, we having. found 40 that other alkali metal'zmcates may be used in our process such as potassium zincate or ammonium'zincate with satisfactory results. The sodium zincate may be prepared by the addition of the calculated amount of .zinc salt -preferably a water-soluble zinc salt for reaterease in manipulation-directly to the sodium hydroxide when the latter is being dissolved in water to form the concentrated or stock solution from which the sodium hydroxide solution is prepared that is used to treat the cellulosic material; or the sodium zincate may be added to this stand- PROCESS FOR TREATING CELLULOSIC MATERIAL.

Application filed December 18, 1926. Serial No. 155,763.

ard sodium hydroxide solution after ,the

same has been adjusted as to. concentration to the degree desired for alkali-cellulose formation with the cellulosic material used; or the alkali metal zincate in alkali metal hydroxide solution in water may be sprayed or otherwise incorporated with the alkalized cellulose during the disintegration of the same in the mixer or Pfleiderer; or the sodium zincate may be added to the xa-nthating churn during, prior or subsequent to the addition of carbon bisulfide to the alkalized cellulose; or the sodium zincate solution may be incorporated with the sodium hydroxide solution used to thin or dilute the xanthated cellulose preparatory to submitting the same to the xanthate ripening or maturin process; or it may be added to the partia ly ripened or immature viscose solution. We have obtained satisfactory results by adding the sodium zincate to each of the stages above mentioned,'but find it more convenient to form sodium zincate by the addition of the required amount of water-soluble zinc salt such as zinc sulfate, directly to the sodium. hydroxide in' the formation of the initial solution of the same, and hence the zincate is present at each stage of the processwp rior to the actual spinning operation. It' will be evident, that adjustment as tothe percentage of zincate incorporated will be made dependent upon whether the zincate is added before or after the'process of mercerization or alkali-cellulose formation wherein a portion of the zincate is removed with the excess of sodium hydroxide solution used, or whether the zincate is added in a step in the process in which no portion of it is removed by a subsequent step in the normal 0 eration of viscose manufacture. We have a ded the water soluble zinc salt to the cellulosic material before the latter has been run intothe sheet form, but find this is not the mostcon- -venient step in the process of viscose manu facture to introduce the zinc.

The process of viscose manufacture is not materially accelerated, inhibited or other- Wise changed as the result of the addition thereto and thereinof the amounts of zincate employed by us, so far aswe have been able to determine. In reality, our research has shown that the addition of the .kali metal hydroxide.

soluble zinc in the process of viscose manufacture, before the finel divided alkali cellulosehas been mature has a tendency to shorten the time of maturing. We have also found this tendency when the coinminuted alkalized cellulose has been ripened in cans made of zinc, and the contents of the cans have been periodically mixed, in order to bring new alkali-cellulose surfaces in contact with the zinc in the presence of free al- One object of the addition of alkali metal zincate in the otherwise normal process of viscose manufacture, is to produce a rayon filament of enhanced luster, additional covering power, increased fiufiiness, and usually a whiter bleached rayon is obtained, than when the process of rayon viscose manufacture is conducted without the introduction of the zincate. Photomicro raphic variations between filaments treate by alkali metal zincates, and a filament not so treated are evident.

It is apparently immaterial whether the water-soluble zinc salt be a chloride, nitrate or sulfate, the relatively small amount of acid radical present after zincate formation. exercising no noticeable effect upon the process or the result obtained. It. is also unmaterial whether the sodium zincate be prepared as such and introduced into the process of viscose manufacture at the step desired, or whether the zincate be formed in the alkali hydroxide. solution employed to mercerizc the cellulose or to dilute and attenuate the xanthated cellulose. In any event, the introduction of zincate 'is made prior to the ri )tlllllg of the viscose to the phase desired for optimum spinning purposes.

In the incorporation of the desired amount of zincate, it has been found advantageous to add the-water-solnble zinc salt such as zinc sulfate in crystal form directly to the caustic soda dissolver, in forming the concentrated stock solution in order that the formation of the sodium zincate may be accelerated, and the formation of zinc hydroxide minimized or prevented, due to the higher temperature and concentration of the canstie in the initial dissolving process. We have obtained satisfactory results in viscose rayon manufacture when the sodium zincate was present in the mercerizing orstee) liquor to the extent of 0.04% to 1.5% but it is to be understood that the percentages above stated may be varied in some adjustments of the process without. departing from the spirit. or essence of our invention. If the zincate is added at any stage of the process subsequent to alkali-cellulose formation and expulsion of excess alkali from the alkali-cellulose formed, a. correspondingly lesser amount will be required. as will be understood by those skilled in the art. We have obtained excellent results over a considerable period of experimentation when the sodium zincate percentage in the steep bath was maintained between the limits of 0.05% to 0.1%. If the zinc is to be added to the dissolving sodium hydroxide which is used for the final solution of the xanthate, the alkali zinc compound should have been previously prepared due to the fact that zinc sulfate when introduced into weak caustic solutions, favors the formation of zinc hydroxide rather than alkali zincates. That is, the alkali metal hydroxide concentration must be sutlicicnt to dissolve zinc hydroxide. From the viewpoint of factory expediency, we do not tiud it preferable to introduce the zincate-compound into the Pfleidcrer during the process of mastication of the alkalized cellulose. or in the xanthate drum during the process of viscose formation.

As an example of carrying our process into effect. we may add to the caustic soda solu-- tion being dissolved for stock solution to be afterwards used for mercerization of cellulosic material. an amount of zinc chloride so that the percentage of sodium zincate in the sodium hydroxide solution 0.05-0.l,2-. plus or minus one-hundredth of one percent. the process being then carried on identical as if the zinc compound had not been present. The viscose rayon produced had an appreciably increased covering power and tlutliness, had a whiter color when submitted to the normal bleaching process. and under the microscope the cross section of individual filaments had to a notable degree the desirable serrated appearance.

Having now dcscribed our invention and in whatmanner it maybe carried into'ellcct. what we claim and desire to secure by Letters Patent is 1. In a process for the manufacture of viscose rayon. the introduction in an alkaline medium into the process of viscose manufacture of an alkali metal zincate in solution, said zincate being incorporated into the alkaline viscose solution prior to the'maturing of the viscose to the stage desired for precipitation, he solution being afterwards forced through openings into a precipitating bath for the formation of filaments, as herein set forth.

2. In a process for the manufacture of viscose rayon, the introduction in an alkaline medium into the process of viscose manufacture of an alkali metal zinc compound in solution in amount insufiieient to cause preeipitation of the viscose and prior to the maturing theviscose to the stage of mcipitation, the solution being afterwar s forced through openings into a settin bath for fill.

ment -mation, as herein set orth.

3. In a process for the manufacture of viscose rayon, the introduction into an alkaline medium into the process of viscose manufacture of an alkali metal zinc comluu llu

pound in solution, said alkali metal zinc compound being incorporated prior to the maturing of the viscose solution to the stage where filaments may be formed, as herein set forth.

4. In a-process for the manufacture of filaments of viscose the introduction in-an alkaline medium into the process of viscose manufacture, of sodium zincate in amount insufficient to cause precipitation of the viscose in solution, said sodium zincate being added at any stage of the process prior to the maturing of the viscose to the stage best suited for spinning purposes, said solution being afterwards forced into a precipitating medium, substantially herein described.

5. In the usual process for the manufacture of viscose intended for the formation of filaments and films, the addition to the caustic soda employed, of alkali metal zincate in amount equivalent to not less than 0.04% of the cellulosic material originally used, substantially as described herein.

6. A process for the manufacture of viscose comprising the usual steps of steeping, disintegratin and mixing, maturing, xanthating, dilutlng with sodium'hydroxide and maturing the diluted xanthate, but in which a portion of the sodium hydroxide normally employed is replaced by a sodium hydroxide solution of sodium zincate in amount equivalent to not less than 0.04% of the cellulose originally employed, as set forth herein.

7. A process for the manufacture of Kenthated cellulose comprisin dissolving an alkali metal zincate in alkai metal hydrox-- ide and using said alkali metal hydroxide in the steps normally necessary to produceviscose for filament and film formation,.as detailed 'herein.

8. A process for the manufacture of mmthated cellulose, comprising steeping, disintegrating and mixing, maturing, xanthating, diluting and ripenin in the usual manner except that instead 0 the employment of sodium hydroxide, there is use a sodium hydroxide-containing sodium zincate dissolved therein, the amount of sodium zincate used being from 0.04% 'to 1.5% on the weight of the cellulose originally used, substantially as set forth herein.

9. In a process for the normal manufacin amount from 0.04% to 1.5%, then disintegrating and mixing, maturing, xanthating, thinning with caustic soda solution and maturing in ways now known, as set forth herein.

11. In a process for the manufacture of viscose productsfrom cellulosic materials, carrying out the usual steps of viscose manufacture up to the point of precipitation'of the ripen'ed viscose, but substituting for a portion of the sodium hydroxide used in the steps preceding the precipitation of the matured viscose, sodium hydroxide, containing an amount of alkali zincate equivalent to 0.04%-1.5% by weight of the original cellulosic material employed, as described herein.

In testimony whereof we afiix our signatures.

HAYDEN B. KLINE.

FRED. o. NIE-DERHAUSER. I 

